Fats and Fatty Acids

CALLIE MAE COONS.

FATS often have been prized articles of diet in man's struggle for food. From early times they have denoted prosperity and hospitality, as when the fatted calf was prepared for merrymaking and the widow shared her oil with the prophet.

Scientific and economic concern about dietary fats goes in cycles.

Sometimes the cycle is geared to war and famine, when fats tend to be scarce and are among the first foods to be conserved and rationed. When food surpluses mount, fats float to the top and are among the first to be used extravagantly.

Pioneers in every civilization have been ingenious in ways of conserving and using fats and in bartering them in international trade. Still today many peoples have a low consumption of fats and oils.

Our food technology in the United States has made possible improved supplies of separated fats and oils from meats, grains, cottonseed, soybeans, peanuts, olives, and coconut.

Agricultural research has led to higher acreage yields of the oilseeds and grains and meat animals of high fatness. The flavors of cooked fats have been imparted to many kinds of processed foods, from roasted nuts to main dishes.

Our total and proportional consumption of fats and oils has climbed to an all-time peak, and the kind and amount of fats we eat have come under the scrutiny of economists and scientists.

Fat makes our meals palatable and satisfying. It is the most concentrated dietary source of energy-9 Calories a gram, compared to 4 Calories in carbohydrate and protein. It promotes efficiency in the utilization of protein and carbohydrate. It facilitates the utilization of fat-soluble vitamins.

Some fats and oils are important sources of vitamins A, D, E, and K. Fats provide various amounts of fatty acids known to be essential in diets and many other fatty acids, which may have nutritional functions that we do not know now.

The amounts of fat, visible and invisible, in food supplies in the United States at retail level have been estimated at 32 percent of the Calories in 1910, 35 percent in 1930, and 40 percent in 1950. They have continued to rise more steeply during the 1950's.

The amounts used in households are much the same about 30 to 33 percent of the Calories before 1900, 35 to 38 in the mid-1930's, and 42 to 44 in the mid-1950's.

Farm families tend to use more fat than city families do, and northern families more than southern families.

As the proportion of Calories from protein has remained about the same an average of 11 to 12 percent at the household level the shift to larger proportions of Calories from fat has been at the expense of carbohydrate.

Thus, in the North Central States, farm families in 1955 had 44 to 46 percent of their Calories from fat and about the same proportion from carbohydrate; 40 years earlier, Calories from fat ran 33 to 35 percent and from carbohydrate 53 to 55 percent.

Families with high incomes tend to have even more Calories from fat than from carbohydrate. Low-income groups select more Calories from carbohydrate.

The few reports of individual food intake the amounts people actually ingest by adults since 1900 indicate 38 to 42 percent of Calories from fat, 45 to 55 percent from carbohydrates, and 13 to 15 percent from protein. The proportions are about the same for women as for men and for the few groups of elderly people on whom reports were made.

These scattered figures on individual intake do not confirm the time trends noted for household diets and retail food supplies, but they confirm the tendency to a high level of intake of fat in the United States.

Figures from chemically analyzed diets and school lunches support the conclusion that the average diet carries more than 40 percent of its Calories from fat and that diets of some individuals carry 50 percent or more.

The fat may drop to 30 percent or even 20 percent of the Calories in times of war or economic stress.

Often 25 to 30 percent is recommended as desirable for any population at any time. The lowest averages reported from any study in the United States, however, was for two groups of families in the southern mountains just after 1900. Their diets contained, respectively, 26 and 30 percent of the Calories from fat, 8 and 9 percent from protein, and 66 and 61 percent from carbohydrate.

People in densely populated countries are said to subsist on such food patterns, often with even less than 30 percent from fats at any time. People in some countries who have fat intakes that are one-third to one-half that in the United States get less than 20 percent of the dietary fat from all animal sources, as much as 40 percent from cereal grains, and 25 percent from peanuts and other oilseeds.

THE SOURCES of fats consumed in the United States follow changing food patterns. The proportions of Calories from dairy and meat products and from separated fats and oils have increased steadily since 1900.

The average household diet in 1955 had about 25 percent of its fats from dairy products; 24 percent from pork products; 14 percent from beef, veal, and lamb; 13 percent from margarines and shortenings; 6 percent from oils and salad dressings; 6 percent from poultry, fish, and eggs; and 12 percent from baked goods, nuts, fruit, and vegetables.

Of the 25 percent from dairy products, more than half was from milk and cheese; 7 percent was from butter, separated from the other milk nutrients; and the rest was from cream and ice cream.

We should bear in mind that natural unseparated fats are associated with the protein, minerals, and vitamins characteristic of the food, as in milk or pork, and also carry some vitamins, such as A, D, and E, which are useful in the metabolism of fats.

How SHALL we choose fats to eat when we have much and many kinds of them in the store and on the table?

Some who want to control weight may be interested in whether the fat is visible (as in butter, shortening, salad oils, and other separated fats or in the visible fat on meat). The fat on meat can be trimmed away, but that means waste. The less readily apparent fats, those mingled, blended, or absorbed into food products, make good eating, but they cannot be trimmed away by the consumer.

Some fats are solid more or less firm at room temperature. Others are plastic. Many come naturally as oils. These characteristics are important for baking, deep frying, and making salad dressings.

Almost any fat can be used for any culinary purposes by suitable adaptations in cooking procedures, however. The melting point of a fat can be altered in many ways by the technologist, but consistency does not always denote properties important in diet.

ONE WILL do well to understand the composition and structure of fats and fatty acids in order to know their complicated role in nutrition. The details are technical, however, and some readers may wish to skip this section.

A pure fat is composed of molecules of glycerol (a trihydroxy alcohol, the same as glycerin), to each of which 1, 2, or 3 fatty acids are linked to form monoglycerides, diglycerides, or triglycerides, respectively.

Fatty acids are hydrocarbons consisting of a chain series of carbons, each of which is able to carry 2 hydrogens, but with 3 hydrogens (methyl group) at one end, and an acid (carboxyl) group at the other end, which connects to the glycerol.

Natural fats, as in meats, grains, and nuts, are made up mostly of triglycerides with only trace amounts of the mono- and di- forms and some free fatty acids. Processed fats, such as hydrogenated commercially hardened shortenings, may contain up to 20 percent of monoglycerides and diglycerides.

It makes some difference nutritionally which fatty acid is attached in the middle position on the glycerol molecule and whether an outer position is open or is linked to another substance.

Much variety in fats comes from the kinds of fatty acids linked to the glycerol whether all three are alike or all are different, whether all are saturated (contain all the hydrogen they can carry) or of various degrees of unsaturation, and whether they are mostly short-chain (under 12 carbons), long-chain (12 to 18 carbons), or extra long-chain (20 carbons or more) fatty acids.

Fatty acids that have 18 carbons in a chain make up about 80 percent and those with 16 carbons comprise about 10 to 15 percent of the fatty acids in average diets.

Short-chain fatty acids occur mostly in milk fat and in coconut oil. Extra long chains occur in fish oils.

Fatty acids that are common in food fats and oils fall into three broad classes according to their degree of saturation.